When pipetting, a liquid that is be pipetted is usually drawn into a chamber of the pipette through the pipette tip, in order to subsequently dispense the liquid in a specifiable quantity through the pipette tip.
For example, DE 26 58 592 A1 discloses a pipette comprising a first chamber, which is arranged in a housing, and a second chamber, which connects to said first chamber and extends to a pipette tip. In this case the pipette tip has an outlet channel, by means of which the first chamber can also be filled with the liquid to be pipetted. At the same time the two chambers are separated from one another by a longitudinally displaceable piston, which has a non-return valve. A chamber non-return valve is disposed upstream of the outlet channel and extends to the second chamber. During aspiration of only one liquid, an auxiliary piston, which is guided in the chamber non-return valve, is removed so that the chamber non-return valve is bypassed.
One disadvantage of the pipettes known from the prior art is that in the course of filling the chambers, the aspiration of the liquid through of the pipette tip may cause contamination. An additional drawback is that during aspiration of the liquid, the gases from the surrounding area come into contact with the liquid, or the ambient air is also drawn in. In particular, when using ultrapure water as the liquid to be pipetted, contact with the atmosphere is disadvantageous, because carbon dioxide is dissolved into the ultrapure water and, in so doing, forms carbonic acid.
Furthermore, U.S. Pat. No. 6,220,835 B1 discloses a dispensing device comprising a first chamber and a second chamber, which connects to said first chamber and extends to an outlet channel, said chambers being separated from one another by a longitudinally displaceable piston having a piston non-return valve. The second chamber has a chamber non-return valve that is arranged upstream of the outlet channel. The first chamber can be filled with a liquid by means of a direct feed line.
The drawback with the known device is that when a liquid, which is to be pipetted, is filled into an intermediate tank, in particular, when ultrapure water is the liquid to be pipetted, the situation may arise that inorganic ions or constituents dissolve out. As a result, the quality of the liquid medium may decline.
GB 221 032 A discloses a syringe or sprayer, which comprises a first and a second chamber in a cylindrical housing, where both chambers are separated from one another by a longitudinally displaceable piston having a non-return valve. A non-return valve is disposed upstream of the second chamber, which is connected to the outlet channel, and extends to the outlet channel. The first chamber can be filled with a liquid by means of a feed line. At the same time the liquid from the first chamber can be drained only through the second chamber and the syringe outlet. On the end facing away from the syringe outlet, the housing has a mount, to which a spare nozzle can be screwed. The spare nozzle is apparently provided for the purpose of replacing the nozzle. The drawback with this known syringe or sprayer is that if a person skilled in this art were to use said syringe or sprayer to fill a liquid, which is to be pipetted, into an intermediate tank, especially if ultrapure water were to be the liquid that is to be pipetted, then the situation might arise that inorganic ions or constituents would dissolve out. As a result, the quality of the liquid medium may decline in an undesired way.
Furthermore, the drawback with the known device is that the piston consists of a first head portion, which does not seal on the periphery and is connected to a piston rod, and a sealing member, which seals and is arranged in such a way that it can be moved longitudinally relative to the head portion. Furthermore, said piston has a through-channel, which is closed by a stop face of the head portion, when the head portion is moved in the direction of the outlet channel.
DE 198 27 035 A1 discloses a dispensing device comprising a first chamber and a second chamber, which connects to said first chamber and extends to a delivery valve, said chambers being separated from one another by a longitudinally displaceable piston having a piston non-return valve. The first chamber can be filled, in particular, with a viscous liquid by means of a direct feed line. This device also has the drawbacks described above.
U.S. Pat. No. 4,118,152 A discloses a dosing pump, which draws a liquid into a first chamber by means of a piston over a suction line and a suction valve and then feeds the liquid through a piston valve into a second chamber and, upon filling the first chamber from the second chamber, discharges the liquid through an outlet. The suction valve and the piston valve have opposing flow directions.
This dosing pump also has the drawbacks described above.
DE 196 32 348 C1 discloses a piston burette, which has a dosing chamber with two valves that are arranged next to each other, a suction valve and a discharge valve. A piston is used to draw in a liquid from a storage tank by way of the suction valve, where in this case the discharge valve is closed, and with the suction valve closed, the liquid is discharged from the dosing chamber by way of the discharge valve that is open.
This dosing pump also exhibits the drawbacks described above.
DE 297 03 080 U1 discloses a device for delivering liquids, which has a non-return valve. The non-return valve is arranged upstream of a discharge tube and consists of a valve ball, which is pressed against a valve seat by a valve spring.